Ultra miniature pressure sensor

ABSTRACT

A method of measuring blood pressure and velocity proximally and distally of a stenosis in a vessel carrying blood includes the steps of providing a guide wire having both a pressure sensor and a velocity sensor disposed on a distal region of the guide wire, introducing the guide wire into the vessel, advancing the guide wire to position the pressure sensor and the velocity sensor proximally and distally of the stenosis, and measuring the blood pressure and velocity proximally and distally of the stenosis with the pressure sensor and the velocity sensor.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. application Ser. No. 11/303,249, filedDec. 15, 2005, which is a continuation of U.S. application Ser. No.10/247,043, filed Sep. 19, 2002, now U.S. Pat. No. 6,976,965, which is acontinuation of U.S. application Ser. No. 09/644,111, filed Aug. 21,2000, now U.S. Pat. No. 6,767,327, which is a continuation of U.S.application Ser. No. 08/912,879, filed Aug. 15, 1997, now U.S. Pat. No.6,106,476, which is a continuation-in-part of U.S. application Ser. No.08/710,062, filed Sep. 9, 1996, now U.S. Pat. No. 5,715,827, which is acontinuation of U.S. application Ser. No. 08/300,445, filed Sep. 2,1994, now abandoned, all of which are hereby expressly incorporated byreference in their entirety.

FIELD OF INVENTION

This invention relates to an ultra miniature pressure sensor and guidewire and apparatus using the same and method, which is particularlysuitable for making pressure measurements in coronary arteries of humanbeings.

It has been well known that it is desirable to make pressuremeasurements in vessels and particularly in coronary arteries with theadvent of angioplasty. Typically in the past, such pressure measurementshave been made by measuring the pressure at a proximal extremity of alumen provided in a catheter advanced into the coronary artery ofinterest. However, such an approach has been less efficacious as thediameters of the catheters became smaller with the need to advance thecatheter into smaller vessels. This made necessary the use of smallerlumens which gave less accurate pressure measurements and in thesmallest catheters necessitated the elimination of such a pressure lumenentirely. In an attempt to overcome these difficulties, ultra miniaturepressure sensors have been proposed for use on the distal extremities ofcatheters. However, it has not been feasible prior to the presentinvention to provide such ultra miniature pressure sensors which arecapable of being incorporated in a guide wire for making pressuremeasurements in a very small arterial vessels. There is therefore a needfor a new and improved ultra miniature pressure sensor and a guide wireand apparatus utilizing the same.

In general it is an object of the present invention to provide an ultraminiature pressure sensor and guide wire and apparatus utilizing thesame making possible pressure and velocity measurements.

Another object of the invention is to provide a sensor which can beutilized on the distal extremity of a guide wire 0.018″ or 0.014″ indiameter.

Another object of the invention is to provide a sensor of the abovecharacter which is formed of a silicon chip of a small dimension whichis reinforced by an additional member to provide reinforcement for thechip.

Another object of the invention is to provide a sensor of the abovecharacter in which a thin diaphragm is formed in the crystalline siliconchip.

Another object of the invention is to provide a sensor of the abovecharacter in which the reinforcing member extends for approximately 200microns beyond the silicon diaphragm.

Another object of the invention is to provide a guide wire with theabove character in which the number of conducting wires required is keptto a minimum.

Another object of the invention is to provide a guide wire and method inwhich simultaneous pressure and velocity measurements can be made.

Another object of the invention is to provide a guide wire of the abovecharacter in which the diaphragm area has been maximized.

Another object of the invention is to provide a guide wire with theabove character in which two pressure sensors are provided on the guidewire which are spaced apart so that pressure measurements can be made onboth sides of a stenosis.

Another object of the invention is to provide a guide wire of the abovecharacter in which the sensors are covered to prevent the formation ofblood clots.

Another object of the invention is to provide an apparatus of the abovecharacter which includes a guide wire with an integral inflatableballoon.

Another object of the invention is to provide an apparatus of the abovecharacter in which temperature compensation can be provided.

Another object of the invention is to provide an apparatus of the abovecharacter which can be utilized in a half-bridge configuration.

Additional features and objects of the invention will appear from thefollowing description in which the preferred embodiments are set forthin detail in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic illustration showing use of a guide wireincorporating a pressure sensor of the present invention and apparatusutilizing the same in conjunction with a patient undergoing acatheterization procedure for diagnosis or treatment.

FIG. 2 is a side elevational view of a guide wire incorporating an ultraminiature pressure sensor of the present invention.

FIG. 3 is an enlarged side elevational view of the distal extremity ofthe guide wire shown in FIG. 2 and showing the pressure sensor mountedtherein.

FIG. 4 is a top plan view looking along the line 4-4 of FIG. 3.

FIG. 5 is a bottom plan view looking along the line 5-5 of FIG. 3.

FIG. 6 is an isometric view of the pressure sensor shown in FIGS. 3, 4and 5 with the lead wires connected thereto.

FIG. 7 is a side elevational view of the pressure sensor shown in FIG.6.

FIG. 8 is a top plan view of the pressure sensor shown in FIGS. 6 and 7.

FIG. 9 is a cross-sectional view taken along the line 9-9 of FIG. 8.

FIG. 10 is a cross-sectional view taken along the line 10-10 of FIG. 8.

FIG. 11 is a cross-sectional view taken along the line 11-11 of FIG. 8.

FIG. 12, is a schematic diagram of the circuitry utilized in thepressure sensor shown in FIGS. 6-11.

FIG. 13 is a side elevational view of the distal extremity of anotherguide wire incorporating the pressure sensor with the sensor of thepresent invention being mounted in the tip housing.

FIG. 14 is a side elevational view of the distal extremity of a guidewire having first and second pressure sensors mounted in the distalextremity of the same spaced apart to permit simultaneous measurementsof proximal and distal pressures with respect to a stenosis.

FIG. 15 is a partial side elevational view of another guide wireincorporating the present invention with an enclosed pressure sensor.

FIG. 16 is a side elevational view partially in section of the distalextremity of another guide wire incorporating the present invention inwhich the pressure sensor is enclosed in a transition housing.

FIG. 16A is a side elevational view in section showing an end-mountedpressure sensor incorporating the present invention.

FIG. 17 is a side elevational view in section of a guide wire housing atip-mounted sensor incorporating the present invention with an integralballoon.

DETAILED DESCRIPTION OF THE INVENTION

In general, the guide wire of the present invention having pressuresensing capabilities is comprised of a flexible elongate element havingproximal and distal extremities and having a diameter of 0.018″ andless. The pressure sensor is mounted on the distal extremity of aflexible elongate element. It is comprised of a crystal semiconductormaterial having a recess therein and forming a diaphragm bordered by arim. A reinforcing member is bonded to the crystal and reinforces therim of the crystal and has a cavity therein underlying the diaphragm andexposed to the diaphragm. A resistor having opposite ends is carried bythe crystal and has a portion thereof overlying a portion of thediaphragm. Leads are connected to opposite ends of the resistor andextend within the flexible elongate member to the proximal extremity ofthe flexible elongate member.

More in particular, the guide wire 21 of the present invention havingpressure measuring capabilities as shown in FIG. 1 is one that isadapted to be used in connection with a patient 22 lying on a table or abed 23 in a cath lab of a typical hospital in which a catheterizationprocedure such as for diagnosis or treatment is being performed on thepatient. The guide wire 21 is used with apparatus 24 which consists of acable 26 which connects the guide wire 21 to an interface box 27.Interface box 27 is connected by another cable 28 to a control console29 which has incorporated as a part thereof a video screen 31 on which awaveform 32 displaying ECG measurements may be provided as well as twotraces 33 and 34 displaying pressure measurements being made by theguide wire 21.

The guide wire 21 is shown more in detail in FIG. 2 and as showntherein, the guide wire 21 can be constructed utilizing the variousconstructions as shown in U.S. Pat. Nos. 5,125,137; 5,163,445;5,174,295; 5,178,159; 5,226,421; and 5,240,437. As disclosed therein,such a guide wire consists of a flexible elongate element 41 having aproximal and distal extremities 42 and 43 and which can be formed of asuitable material such as stainless steel having an outside diameter forexample of 0.018″ or less and having a suitable wall thickness as forexample, 0.001″ to 0.002″ and conventionally called a “hypotube” havinga length of 150-170 centimeters. Where a smaller guide wire is desired,the hypotube 41 can have an exterior diameter of 0.014″ or less.Typically such a guide wire includes a core wire (not shown) of the typedisclosed in the above identified patents which extends from theproximal extremity to the distal extremity of the flexible elongateelement 41 to provide the desired torsional properties for guide wires(See U.S. Pat. No. 5,163,445, col. 18:40-51) to facilitate steering ofthe guide wire 21 in the vessel.

A coil spring 46 is provided and is formed of a suitable material suchas stainless steel. It has an outside diameter of 0.018″ and is formedfrom a wire having a diameter of 0.003″. The spring 46 is provided witha proximal extremity 47 which is threaded onto the distal extremity 43of the flexible elongate member 41. The distal extremity 48 of the coilspring 46 is threaded onto the proximal extremity 49 of an intermediateor transition housing 51 such as disclosed in U.S. Pat. No. 5,174,295,formed of a suitable material such as stainless steel having an outsidediameter of 0.018″ and having a suitable wall thickness as for example,0.001 ″ to 0.002″. The housing 51 is provided with a distal extremity 52which has the proximal extremity 53 of a coil spring 54 threadedthereon. The coil spring 54 is formed of a highly radiopaque materialsuch as palladium or a tungsten platinum alloy. The coil spring 46 canhave a suitable length as for example 27 centimeters whereas, the coilspring 54 can have a suitable length such as 3 centimeters. Theintermediate or transition housing 51 can have a suitable length as forexample, one to five millimeters. The use of the two coils 46 and 54 onopposite ends of the housing 61 provides a very flexible floppy tip forthe guide wire 21 as described in U.S. Pat. No. 5,174,295. The coil 54is provided with a distal extremity which is threaded onto an end cap 57also formed of a suitable material such as stainless steel and having anoutside diameter of 0.018″ and a wall thickness of 0.001″ to 0.002″. Anultrasonic transducer 58 is mounted in the end cap in a manner describedin U.S. Pat. No. 5,125,137 and has conductors 61 and 62 secured to thefront and rear sides of the same which extend interiorly to the proximalextremity of the flexible elongate member 41.

A torquer 66 of the type described in U.S. Pat. No. 5,178,159 is mountedon the proximal extremity 42 of the flexible elongate member 41 forcausing a rotation of a guide wire 21 when used in connection withcatheterization procedures in a manner well known to those skilled inthe art.

The proximal extremity 42 is also provided with a plurality ofconducting sleeves (not shown) of the type disclosed in U.S. Pat. No.5,178,159. In the present invention, one or more additional sleeves canbe provided to make connection to the conductors hereinafter described.The proximal extremity 42 of the flexible elongate member is removablydisposed within a housing 68 of the type described in U.S. Pat. Nos.5,178,159, 5,348,481 and 5,358,409 that makes electrical contact withthe sleeves on the proximal extremity 42 while permitting rotation ofthe sleeves and the flexible elongate member 41. The housing 68 carriesfemale receptacles (not shown) which receive the sleeves and which areconnected to a cable 71 connected to a connector 72. The connector 72 isconnected to another mating connector 73 carried by the cable 26 andconnected into the interface box 27.

The portion of the guide wire 21 therefore described is substantiallyconventional. In accordance with the present invention it is providedwith a pressure measuring capability in the form of a pressure sensorassembly 76 which is mounted within the intermediate or transitionhousing 51. The pressure sensor assembly 76 consists of a diaphragmstructure 77 supported by a base plate 78. The diaphragm structure 77 isformed of suitable materials such as “n” type or “p” type 100 orientedsilicon with a resistivity of approximately 6-8 ohm-centimeters. Thediaphragm structure 77 is a die made from such a wafer. In accordancewith the present invention, the die has a suitable length, as forexample, 1050 microns and for a 0.014″ guide wire has a width of 250microns and for a 0.018″ guide wire has a width of between 250 and 350microns. It can have a suitable thickness, as for example, 50 microns. Arectangular diaphragm 79 is formed in the diaphragm structure 77 of asuitable thickness, as for example, 2.5 microns and having dimensionssuch as a length of 350 microns. The diaphragm 79 has first and secondor top and bottom surfaces 80 and 81. The diaphragm is formed byutilization of conventional masking and crystal etching techniques whichcreate a die with two parallel sloping endwalls 82 and two parallelsidewalls 83 extending at right angles to the end walls 82 leading downto the top surface 80 of the diaphragm 79 to form a well 84. Ashereinafter explained, the diaphragm 79 is made relatively wide incomparison to the diaphragm structure 77 so that what remains is arelatively narrow rim 86 formed by side portions 87 and 88 and an endportion 89. As can be seen from FIGS. 6, 7 and 8, the diaphragm 79 islocated at or near one end of the diaphragm structure or die 77. It hasbeen found that it is desirable to provide a rectangular geometry forthe diaphragm 79 rather than a square geometry in order to obtain thehighest possible sensitivity for pressure measurements. For example, ithas been found that the rectangular diaphragm provides approximately 1.5times more sensitivity than does a square diaphragm for the samediaphragm thickness and width.

In etching the well 84 to form the diaphragm 81, an impurity can beimplanted into the backside of the diaphragm structure 77 before theetching process is commenced so that etching will stop at the desireddepth, as for example, within 2 to 3 microns of the bottom surface 81 toprovide a diaphragm 79 having a thickness ranging from 2 to 5 microns,and for example, the preferred thickness of 2.5 microns. Because the rim86 provided on the diaphragm structure 77 surrounding the rectangulardiaphragm 79 is relatively thin, the base plate 78 provides support forthis rim to provide the necessary strength for the pressure sensor 76.

In order to obtain adequate performance characteristics such assensitivity in the miniaturized pressure sensor assembly 76 hereinbeforedescribed, it has been found desirable to have as much of the width ofdiaphragm structure 77 as possible be occupied by the diaphragm 79 andat the same time to minimize the portion of the diaphragm structure 77occupied by the rim. In order to achieve a diaphragm width ratio of atleast 0.45 to 0.9 with respect to the width of the diaphragm 79 to thewidth of the structure 77 and therefore to obtain the largest diaphragmpossible in the diaphragm structure 77, diaphragm 79 is made relativelylarge compared to rim 86. With current manufacturing technology, it hasbeen found feasible to have a width of rim 86 of 40 microns, whichprovides for a diaphragm 79 of 170 microns in a 250 micron-widediaphragm structure 77 to provide a diaphragm width ratio of 0.68. In alarger diaphragm structure such as 350 microns wide, the pressure sensorassembly 76 can be made stronger by increasing the rim width to 90microns. Alternatively, it can be made more sensitive by increasing thediaphragm width up to 270 microns. This results in a diaphragm widthratio for a 350 micron-wide device of between 0.49 and 0.77, dependingon what combination of sensitivity and strength is desired.

Prior to or after the formation of the rectangular diaphragm 79, aplurality of V-shaped recesses or grooves 91 are formed in the diaphragmstructure 77 on the end opposite the end at which the diaphragm 79 islocated and on the side opposite the side in which the well 84 isformed. These V-shaped recesses 91 also can be formed in a conventionalmanner by the use of a conventional etch. It should be appreciated thatif desired, the etching can be stopped so that the recesses formed areshort of a complete V. By way of example, if the etching for theV-shaped recess was stopped at a depth of 12 microns, the bottom of thesubstantially V-shaped recess or trench 91 would be approximately 8microns wide.

After the V-shaped or substantially V-shaped recesses have been formed,a P+ diffusion utilizing a suitable material such as boron can becarried out to create a V-shaped region 92 (in the structure 77) whichunderlies the V-shaped recess 91. Utilizing suitable masking a commonlayer 93 of a suitable material such as chromium is sputtered into theV-shaped recess 91 to a suitable thickness as for example, 300 Angstromsfollowed by a layer 94 of a suitable material such as gold of a suitablethickness as for example 3000 Angstroms. The layers 93 and 94 overliethe bottom surface 81 to form pads 96 thereon. In depositing the gold inthe V-shaped recess 91 it is desirable to terminate the gold just shortof the leftmost extremity of the V-shaped recess as viewed in FIG. 8 inorder to minimize the likelihood of lead-to-lead shorting during thedicing operation when a wafer is sawed up into individual sensor chips.

By way of example, the spacing between V-grooves 91 from center tocenter can be 75 microns with the V-groove having a width of 25 micronsand having a typical depth of 18 microns. The metal pads 96 formed bythe chromium and gold layers 93 and 94 can have a suitable width as forexample, 50 microns with the overlap on each side being approximately12.5 microns to provide a spacing of approximately 25 microns betweenadjacent V-shaped pads 96. The bottom of the V-shaped groove can have atotal length of approximately 250 microns.

The regions 92 formed from the P+ diffusion have patterns that extend tothe right from the three V-shaped recesses 91 as viewed in FIG. 8 for adistance so that they underlie the approximate midpoint of the diaphragm81 on opposite sides to provide generally U-shaped portions or resistors92 a which are located on the diaphragm in areas of a maximum stress toprovide maximum sensitivity to pressure changes. The resistors 92 a areprovided with opposite ends, one end being connected to one each of theV-grooves and the other end being connected to the center or commonV-groove. Contact is made to these P+ diffused regions by the chromiumand gold layers 93 and 94 hereinbefore described.

The base plate 78 can be formed of a suitable material such as Pyrexsupplied by Corning Glassworks and can have the same width as thediaphragm structure 77 but has a length which is less than the length ofthe diaphragm structure 77 so that the V-shaped grooves 91 are exposedon the underside of the diaphragm structure 77 as shown in FIG. 6. Italso can have a suitable length such as 850 microns. It is provided witha rectangular recess or cavity 101 having substantially the same size asthe diaphragm 79. It can be etched into the Pyrex by suitable means suchas a conventional etching process utilizing hydrochloric acid. After theetching has been completed to form the rectangular recess 101 it isbonded to the lower surface of the diaphragm structure 77 to form ahermetic seal with respect to the same so that the cavity 101 underliesthe diaphragm 79 and is exposed to the bottom surface 81 of thediaphragm 79. The cavity 101 below the diaphragm 79 serves as areference pressure chamber and can be filled with a suitable fluid. Forexample, it can be filled with air to half an atmosphere to provide apartial vacuum. Alternatively, the cavity 101 can be filled to oneatmosphere or it can be completely evacuated.

A trifilar lead structure 106 is connected to the rectangular diaphragmstructure 77. It has insulated copper leads 107 of a suitable diameteras for example 48 AWG soldered into place to the V-shaped recesses 91 sothat the leads 107 extend outwardly therefrom and lie in a planeparallel to the plane of the diaphragm structure 77. The trifilar leadconstruction 106 provides insulation around each lead and in additionthere is provided additional insulation which surrounds the leads andwhich interconnects the leads into a single unit which can be readilyextended through the hypotube forming the flexible elongate member 41.

The pressure sensor assembly 76 is mounted within a cutout 111 providedin the transition housing 51 and secured therein by suitable means suchas an epoxy 112 so that the outer surface of the pressure sensorassembly 76 is generally flush with the outer surface of the transitionhousing 51 (see FIG. 3) and so that the diaphragm 79 is exposed toambient and the leads 106 extend through the flexible elongate member 41to the proximal extremity 42 of the same where they are connected to thesleeves (not shown) carried by the proximal extremity 42 disposed withinthe housing 68. Also, the conductors 61 and 62 of the velocity sensingtransducer 58 are connected to two of such sleeves (not shown) providedon the proximal extremity 42.

A schematic of the wiring for the pressure sensor assembly 76 is shownin FIG. 12. The two generally U-shaped portions 92 a on opposite sidesof the diaphragm 79 are represented as resistors and are connected tothe three leads 107 in the manner shown. One of the first of the outsideleads 107 is “SIGNAL OUT” (+) and the second or other outside lead is“SIGNAL OUT” (−) and the third or middle lead is a common lead as shown.This pattern makes it possible to not cross leads and has the third leadgoing up the middle or center of the die or the diaphragm structure 77.It can be seen that the two resistors 92 a connected as shown form ahalf bridge one of the resistors responds positively to pressure changeand the other resistor responds negatively to a pressure change. Thus,as a pressure is supplied to the diaphragm 79, one resistor increases invalue and the other resistor decreases in value to provide a voltagechange. By applying the same current to both resistors at the same time,temperature effects can be measured because temperature change willaffect both of the resistors in the same way so that the pressuremeasurements can be compensated for any changes in temperature which aresensed by the resistors 92 a. The changes in resistivity caused by thetemperature changes in the resistors will cancel each other out becauseof the half bridge configuration used. In connection with FIG. 12 it canbe seen that with the use of three leads it is possible to obtaintemperature compensation by utilizing a half-bridge configuration forthe pressure sensor. Alternatively, a more precise temperaturecompensation can be provided by directly measuring the two resistances,and then solving the mathematical equations which relate temperature andpressure to the two sensor resistances.

Operation and use of the guide wire 21 in performing a catheterizationprocedure such as angioplasty may now be briefly described as follows:Let it be assumed that a guiding catheter (not shown) has beenintroduced into the femoral artery of the patient 22 shown in FIG. 1with the distal extremity near the desired location in the heart inwhich it is desired to perform an angioplasty. The guide wire 21 of thepresent invention is inserted into the guiding catheter. At the timethat its distal extremity is in close proximity to the distal extremityof the guiding catheter, the pressure output signal from the guide wireis compared with that of the guiding catheter assuming that the guidewire is provided with pressure sensing capabilities. If there is adifference between the two pressure measurements, the pressuremeasurement from the guide wire 21 is equalized with that from theguiding catheter at the control console 29. The distal extremity of theguide wire 21 is then advanced so that it is proximal of the stenosis tobe treated at which time a pressure measurement is made. After thispressure measurement has been recorded, the distal extremity of theguide wire is then advanced through the stenosis and another pressuremeasurement made to determine whether the stenosis is severe enough torequire treatment by angioplasty. Alternatively, the distal extremity ofguide wire 21 can be immediately advanced to the distal side of thestenosis rather than making a pressure measurement proximal of thestenosis and thereafter comparing the pressure measurement on the distalextremity being measured by the guide wire 21 with the pressuremeasurement being provided proximal of the stenosis by the guidingcatheter. If it is determined that the stenosis causes a partialocclusion which is severe enough to warrant use of an angioplastyprocedure, an angioplasty catheter having a balloon thereon (not shown)can be advanced over the guide wire 21 and advanced into the stenosis todilate the stenosis. After dilation has occurred, the angioplastyballoon can be withdrawn from the stenosis and pressure measurements canbe made proximal and distal of the stenosis to ascertain the effect ofthe angioplastic treatment. If the pressure measurements indicate thatthe original dilation by the angioplasty balloon has been inadequate,another balloon catheter as for example, one having a balloon of agreater diameter can then be positioned over the guide wire 21 byutilizing an exchange wire if appropriate. The larger angioplastycatheter can be advanced through the stenosis and inflated to againdilate the stenosis to a larger size after which it can be withdrawn.Thereafter, pressure measurements proximal and distal of the stenosiscan again be made to ascertain whether or not the second dilation whichhas been performed is adequate. The decisions to be made in connectionwith such procedures can be readily made by use of the control console29 by observing the traces 33 and 34 on the video monitor 31.

It also should be appreciated that at the same time Doppler velocitymeasurements can be made by the transducer 58. That information can beused in connection with the pressure measurements to ascertain the needfor performing the angioplasty procedure or for determining the efficacyof the angioplasty procedure performed. Because of the very smalldiameters of the guide wires as for example, 0.018″ or 0.014″, it ispossible to utilize the guide wire 21 of the present invention with verysmall coronary vessels in the heart. In connection with the leads fromthe Doppler transducer 58 it should be appreciated that if desired someof the conductors provided for the Doppler ultrasound transducer can beshared with the wires or conductors provided for the pressure sensorassembly 76. Thus, two of the wires for the pressure sensor can beutilized for the Doppler transducer because the pressure sensor operatesat DC or up to a few hundred Hz or KHz whereas the Doppler sensoroperates at 10 MHz and above. These frequency ranges can be readilyseparated by one skilled in the art by using simple filters and theappropriate circuitry.

In connection with the present invention it should be appreciated thatrather than bonding the leads 107 into the V-grooves or V-shapedrecesses 91, the Pyrex base plate 78 can be formed so it has the samelength as the diaphragm structure 77. V-shaped or U-shaped grooves canbe formed in the base plate underlying the V-shaped grooves to in effectform little tunnels which can be utilized for receiving the wires 107and for them to be soldered therein. Such a construction aids in theplacement of wires which are of the very small diameter, as for example,1 mil.

Another embodiment of a guide wire 121 incorporating the presentinvention is shown in FIG. 13. In the guide wire 121, pressure sensorassembly 76 is mounted in a tip housing 122. The tip housing 122 can besubstituted at the end cap 57 and threaded into the distal extremity 56of the coil 54. The tip housing 122 can be formed of a suitable materialsuch as stainless steel having an outside diameter of 0.018″ and a wallthickness of 0.001 ″ to 0.002″. The sensor assembly 76 can be of thetype hereinbefore described and can be mounted in a cutout 123 providedin the tip housing 122 much in the same manner as the sensor assembly 76was mounted in the cutout 111 in the transition housing 51 such as byuse of an epoxy 124. An hemispherical end cap 126 formed of a radiopaquematerial such as palladium or tungsten platinum alloy can be mounted onthe distal extremity of the tip housing 122. Alternatively, the end cap126 can be formed of a non-radiopaque material such as epoxy or siliconerubber.

Thus it can be seen with the embodiment of the guide wire 121 shown inFIG. 13, the guide wire 121 can be utilized in the same manner as theguide wire 21 hereinbefore described with the exception of it cannot beused for making velocity measurements because that capability has beenremoved from the guide wire 121.

Another guide wire 131 incorporating the present invention is shown inFIG. 14 in which two pressure sensors 76 have been provided. The sensors76 have been spaced apart a suitable distance as for example, 3centimeters with one of the pressure sensors being mounted in thetransition housing 51 and the other pressure sensor being mounted in atip housing 122 of the type shown in FIG. 13. With such an arrangement,it can be seen that the distal extremity of the guide wire 131 can beadvanced across a stenosis in a vessel with the pressure sensor 76mounted in the tip housing being distal of the stenosis to measuredistal pressure and the pressure sensor 76 in the transition housing 51being proximal of the stenosis to measure proximal pressure. Thus, itcan be seen that it is possible to measure simultaneously the distalpressure and the proximal pressure with respect to a stenosis in avessel. This may give more accurate measurements than utilizing theproximal pressure being sensed by the guiding catheter.

When using two pressure sensors 76 in the same guide wire as shown inFIG. 14, it is possible to utilize the same common wire for both of thetransducers, thus making it necessary to provide only five wires ratherthan six wires for the two pressure sensors.

Still another guide wire 141 incorporating the present invention isshown in FIG. 15 in which a cover 142 is provided for covering thepressure sensor assembly 76 provided in the transition housing 51. Thecover is elongate and extends the length of the cutout 111 and isarcuate in cross-section so that it conforms to the conformation of thetransition housing 51. The cover 142 can be secured in place by asuitable means such as an adhesive. The cover 142 overlying the pressuresensor assembly 76 is provided with a pin hole 143 which immediatelyoverlies the diaphragm 79. The pin hole 143 can be of a suitable size asfor example 2-5 mils in and preferably 3 mils in diameter. The cover 142serves to prevent the large opening provided by the cutout 111 fromcollecting blood which could possibly clot. The cover 142 also serves toprotect the sensor 76 from damage. It also prevents the sensor 76 frombeing broken loose during use of the guide wire 141. It should beappreciated that if desired, the volume beneath the cover 142 can befilled with viscous fluid such as oil which can be utilized fortransmitting pressure from the pin hole 143 to the diaphragm 81. With asmall size pin hole 143, the viscous fluid provided would not have atendency to bleed out of the transition housing 51. The viscous fluidwould be held in place because of the surface tension of the fluid.Because there is a very short distance between the pin hole 143 and thediaphragm 79, there would be very little tendency for the viscous fluidto damp any pressure signal transmitted from the blood in which theguide wire 141 is disposed to the diaphragm.

Another guide wire 151 incorporating the present invention is shown inFIG. 16 having a transition housing 152 formed of a suitable materialsuch as stainless steel and having an OD of 0.018″ or less. A pressuresensor assembly 76 of the type hereinbefore described is mounted withinthe bore 153 of the transition housing 152 and is secured therein bymounting the same in an epoxy 154 while leaving the area immediatelyabove the diaphragm 79 exposed to a pin hole 156 provided in thetransition housing 152. The space overlying the diaphragm 81 exposed tothe pin hole 156 can be filled with a viscous fluid 157 such as oil. Theviscous fluid 157 can be retained within the desired location by abarrier 158 formed on the proximal side of the pressure sensor 76 havingthe trifilar lead structure 106 extending therethrough, in sealingengagement therewith. To seal the other end of the bore 153, anintermediate end cap 161 can be provided which is provided with abarrier 182 extending thereacross to seal the bore 153. The intermediateend cap 161 can be bonded to the transition housing 152 by a suitablemeans such as an adhesive (not shown). The coil 54 can be threaded ontothe intermediate end cap 161 and can be threaded onto a tip housing 166that carries a rounded hemispherical tip 167. With such a constructionit can be seen that the pressure sensor assembly 76 is protected withinthe transition housing 152.

In FIG. 16A a guide wire 168 is shown which is very similar to the guidewire 151 with the exception that the housing 152 has been provided onthe distal extremity of the coil 46 with the tip 167 directly mounted onthe housing 152 for closing the bore 153.

In FIG. 17 there is shown another embodiment of a guide wire 171incorporating the present invention which has an integral ballooncarried thereby. A guide wire with an integral balloon is described inU.S. Pat. No. 5,226,421. The guide wire 171 consists of a flexibleelongate tubular member 173 in a manner formed of a suitable materialsuch as plastic which is provided with a distal extremity 174. Aninflatable balloon 176 is secured to the distal extremity 174 of theflexible elongate member 173 in a manner well known to those skilled inthe art. Such a balloon can be formed integral with the distal extremityand can be formed of the same material as the flexible elongate tubularmember 173. Alternatively, it can be formed of a different material orthe same material and be formed as a separate part and secured to thedistal extremity 174 by suitable means such as adhesive.

The balloon 176 is provided with a distal extremity which is closed andwhich is secured to the proximal extremity of a coil spring 178 formedof a radiopaque material such as a palladium or tungsten platinum alloythreaded onto a tip housing 179. The tip housing 179 can be formed in amanner similar to the tip housing 122 shown in FIG. 13 having a pressuresensor 76 mounted therein and carrying an end cap 181. The trifilarleads 106 connected to the sensor 76 extend through the coil 178 andthrough the balloon 176 and through the flexible elongate tubular member172 to the proximal extremity thereof. A core wire 186 formed of asuitable material such as stainless steel is provided in the flexibleelongate member 173 and can be provided with a diameter such asdisclosed in U.S. Pat. No. 5,226,421. The core wire 186 is provided witha tapered portion 186 a extending through the balloon which has a distalextremity secured to the housing 179 by a suitable means such as theepoxy utilized for mounting the sensor 76 within the housing. Theflexible elongate tubular member 172 is provided with a ballooninflation lumen 187 which can be used for inflating and deflating theballoon 176.

The guide wire 171 with an integral balloon 171 can be utilized in amanner similar to that hereinbefore described for the other guide wires.Rather than deploying a separate catheter with a balloon thereon overthe guide wire, the guide wire 171 itself carries the balloon 176 whichcan be inflated to dilate the stenosis after the proximal and distalpressure measurements have been made by the tip mounted sensor 76. Afterthe balloon 176 has been deflated, the pressure measurement can be madeto ascertain the pressure in the distal extremity after dilation hasoccurred. If necessary, the balloon 176 can be re-inflated to performanother dilation of the stenosis to obtain improved blood flow throughthe stenosis.

After an appropriate dilation has occurred, the guide wire 171 withintegral balloon can be removed in a conventional manner. Theangioplasty procedure can then be completed in a conventional manner.

From the foregoing, it can be seen that there has been provided an ultraminiature pressure sensor which can be utilized on guide wires having adiameter of 0.018″ and less which can be utilized for making accuratemeasurements proximal and distal of a stenosis in the coronary vessel.This is made possible because of the small size of the pressure sensorincorporated into the distal extremity of the guide wire. In addition tosensing pressure, flow velocity can also be obtained by the use of adistally mounted velocity transducer provided on the same guide wire ason which the pressure sensor is mounted. Alternatively, additional firstand second pressure sensors can be provided on the distal extremity of aguide wire so that pressure measurements can be made simultaneously,proximally and distally of the stenosis. The pressure sensor isconstructed in such a manner so that it can be readily incorporatedwithin the confines of a small guide wire as for example, 0.018″ andless. It can be constructed to avoid a large opening in the distalextremity of the guide wire to inhibit or prevent the formation ofclots. The pressure sensor also can be protected so that it cannot bereadily damaged or broken loose. In addition, where desired, the guidewire can be provided with an integrally mounted balloon on its distalextremity so that the guide wire can be utilized for performing anangioplasty procedure while at the same time facilitating the making ofpressure measurements, proximal and distal of the stenosis beingtreated.

1. An apparatus for measurement of a plurality of flow-relatedcharacteristics comprising: a guidewire having an outside diameter of0.018″ or less; a first sensor disposed in a distal region of theguidewire for measuring a first characteristic of flow; and a secondsensor disposed in a distal region of the guidewire for measuring asecond characteristic of flow, wherein the first sensor and secondsensor are configured for measuring the first characteristic and thesecond characteristic simultaneously.
 2. The apparatus of claim 1,wherein the first sensor is a pressure sensor.
 3. The apparatus of claim1, wherein the second sensor is a velocity transducer.
 4. The apparatusof claim 1, further comprising a sensor housing having an external wall,a lumen, and a hole in the external wall extending from an externalsurface of the sensor housing to the lumen and being open to ambientfluid.
 5. The apparatus of claim 4, wherein the sensor housing isdisposed near a distal extremity of the guidewire.
 6. The apparatus ofclaim 1, further comprising a first coil disposed proximally from thesensor housing.
 7. The apparatus of claim 6, further comprising a secondcoil comprising a radiopaque material and the second coil disposeddistally from the sensor housing.
 8. The apparatus of claim 1, whereinthe first sensor comprises a solid state pressure sensor.
 9. Theapparatus of claim 8, wherein the solid state pressure sensor has apressure sensitive region located at or near one end thereof.
 10. Theapparatus of claim 8, wherein the solid state pressure sensor apparatusis mounted within the sensor housing such that the pressure sensitiveregion projects into the lumen of the sensor housing without containingthe external wall of the sensor housing and that such a portion of thepressure sensitive region is disposed opposite the hole and is in fluidcommunication with the ambient fluid via the hole.
 11. The apparatus ofclaim 8, wherein the solid state pressure sensor is mounted within thesensor housing using an elastic medium.
 12. The apparatus of claim 11,wherein the elastic medium is an epoxy.
 13. The apparatus of claim 9,wherein the pressure sensitive region includes a pressure sensitivediaphragm.
 14. The apparatus of claim 1, wherein the solid statepressure sensor comprises a diaphragm structure supported by a baseplate.
 15. The apparatus of claim 1, further comprising a core wireextending from a proximal extremity of the guidewire, through the sensorhousing, and to the distal extremity of the guidewire.
 16. The apparatusof claim 15, wherein the core wire comprises a tapered distal extremity.17. The apparatus of claim 4, wherein the lumen is filled with viscousfluid.
 18. The apparatus of claim 17, wherein the viscous fluidcomprises an oil.
 19. The apparatus of claim 17, wherein the hole has adiameter configured to hold the viscous fluid within the lumen andprevent bleeding of the viscous fluid into the ambient fluid.
 20. Theapparatus of claim 19, wherein the hole has a diameter of approximately5 mils or less.
 21. The apparatus of claim 1, further comprising atemperature sensitive resistor disposed on a distal extremity of theguidewire.
 22. A method for measurement of a plurality of flow-relatedcharacteristics comprising the steps of: providing a guidewire havingthe first sensor and a second sensor disposed in a distal region of theguidewire; inserting at least a portion of the guidewire into a bloodvessel; advancing the distal region of the guidewire distal to astenosis; and simultaneously measuring a first characteristic of flowwith the first sensor and a second characteristic of flow with thesecond sensor.
 23. The method of claim 22, wherein the first sensor is apressure sensor.
 24. The method of claim 22, wherein the second sensoris a velocity transducer.
 25. The method of claim 22, wherein theguidewire has a core wire extending from a proximal region to the distalregion of the guidewire.
 26. The method of claim 23, wherein the firstsensor measures blood pressure.
 27. The method of claim 24, wherein thesecond sensor measures velocity.
 28. The method of claim 23, wherein thepressure sensor operates at a relatively low frequency.
 29. The methodof claim 24, wherein the velocity transducer is operated at a frequencyon the order of 10 MHz.
 30. The method of claim 22, wherein the pressuresensor and velocity transducer are coupled to a common set ofconductors.
 31. The method of claim 22, wherein the pressure sensor andvelocity transducer are coupled to a common set of conductors.
 32. Themethod of claim 22, wherein the step of measuring blood pressure andvelocity comprises the steps of: measuring the blood pressure andvelocity proximally of the stenosis, and subsequently measuring theblood pressure and velocity distally of the stenosis.
 33. The method ofclaim 22, wherein the step of measuring blood pressure and velocitycomprises the steps of: measuring the blood pressure and velocitydistally of the stenosis, and subsequently measuring the blood pressureand velocity proximally of the stenosis.
 34. The method of claim 22,further comprising the steps of: advancing an angioplasty catheterhaving a balloon thereon over the guidewire to the location of thestenosis, and dilating the stenosis with a balloon.